The present invention, in some embodiments thereof, to compositions and methods for preventing and treating growth of abnormally growing cells using anti-CD24 monoclonal antibodies, and more particularly, to the use of anti-CD24 in combination with cytotoxic chemotherapeutic agents for prevention and treatment of colorectal and pancreatic cancers.
CD24:
CD24 has been described in a growing body of literature in relation to cancer, over-expressed in various human malignancies. Its expression is often correlated with a poor prognosis. Recently, using gene expression array, increased expression of CD24 in transformed, but not non-transformed, enterocytes that was down regulated to a normal level of expression following short (72 hours) and long (six months) exposures to a selective COX2 inhibitor, celecoxib (Celebrex, Pfizer, NY) was observed. The results were validated by immunohistochemical stainings in 389 human samples derived from a variety of GI malignancies. A strong membrane expression of CD24 protein was seen already at an early stage of carcinogenesis, the adenomatous polyp. CD24 was expressed in 90.7% of adenomas, and 86.3% of CRC cases, while very low levels of expression were observed in normal epithelium. The upregulation of CD24 during colorectal cancer (CRC) progression, and its downregulation by a known chemopreventive agent (COX2 inhibitor) suggested the possibility that CD24 could be important in the oncogenic pathway.
The CD24 gene encodes a heavily glycosylated cell-surface protein, anchored to the membrane by phosphatidylinositol. Human CD24 consists of 31 amino acids with 16 potential O- and N-glycosylation sites. CD24 plays a crucial role in cell selection and maturation during hematopoiesis. It is expressed mainly on premature lymphocytes, certain epithelial and neural cells. It also plays a role during the embryonal development of neural and pancreatic cells. Analysis of biochemically separated glycolipid-enriched membrane (GEM) fractions indicated enhanced association of CD24 and Lyn protein tyrosine kinase in GEM, as well as increased Lyn kinase activity after CD24 cross-linking, suggesting that the CD24 receptor mediates intracellular signaling even though it has no trans-membrane domain. CD24 is also known to be an alternative ligand for P-selectin and thus might function in metastases shedding. Anti-CD24 monoclonal antibodies (mAb) induced growth inhibition in lymphocytes precursors.
Studies have shown that CD24 expression could potentiate homotypic B-cell aggregation and heterotypic adhesion to activated endothelium. Under physiological conditions, CD24 over-expression enhanced cancer cells rolling on and invading through vessel-walls by increasing their adherence to platelets and endothelial cells. Thus, within the tumor micro-environment, CD24 binding with P-selectin enhances tumor development, since P-selectin was found to be crucial in CRC carcinogenesis. In P-selectin deficient mice vs. normal mice, human CRC cells injected subcutaneously into mice proliferated more slowly and produced fewer lung metastases at intra-venous injection, suggesting that the mucin-dependent interaction with P-selectin is an important feature of CRC cells.
Bauman et al. showed that ectopic over-expression of CD24 in a rat-carcinoma cell line increases cell proliferation and adhesion through activation of integrins. Similarly, Smith et al. have shown how transient down-regulation of CD24 expression in human carcinoma cell lines resulted in growth inhibition and reduced clonogenicity and cell migration through a change in the actin cytoskeleton in several epithelial cancer cell lines (breast, urothelial and prostate carcinomas and osteosarcoma).
Patents and patent applications relating to CD24 and cancer include: U.S. Pat. No. 7,115,360 to Clarke et al; U.S. Pat. No. 6,984,522 to Clarke et al.; U.S. Pat. No. 6,171,798 to Levine et al; U.S. Pat. No. 5,952,471 to Lawson; U.S. Pat. No. 6,146,628 to Uckun et al.; U.S. patent application Ser. No. 12/033,557 to Agarwal; U.S. patent application Ser. No. 10/913,905 to Hsing-Chang et al; U.S. patent application Ser. No. 12/019,339 to Wicha et al; and U.S. patent application Ser. No. 11/607,780 to Clarke et al.
Colorectal Cancer:
Colorectal cancer (CRC) represents a major public health problem accounting for over 1 million cases of new cancers and about half a million deaths worldwide. Despite curative surgery in those presenting early, the risk of recurrence is significantly high. In colon cancer, chemotherapy is the principal adjuvant therapy and the addition of radiotherapy to chemotherapy has not been shown to improve outcome. Recently, newer drugs with significant impact in the treatment of metastatic CRC such as irinotecan, oxaliplatin and oral fluoropyrimidines have all completed phase III randomised testing in the adjuvant setting of colon cancer.
Antibody Anti-Cancer Therapy:
There are many potential advantages to the application of antibodies to anti-cancer treatment. Antibodies are typically much more specific in targeting cancerous cells than metabolic drugs or radiotherapy, and as such typically have fewer and less sever side effects. In addition, monoclonal antibodies can be designed to target antigens characteristic of individual stages or forms of cancers, affording opportunity to customize therapy to the individual patient's disease profile.
Many clinical trials of anti-cancer antibody therapy have been undertaken, indicating good outcomes with fewer side effects as compared to chemotherapy or radiotherapy. A growing number of therapeutic monoclonal antibodies have been approved for clinical use by the FDA, such as Ritaximab, Ibritumomab and Tositumomab for Non-Hodgkins Lymphoma, Trastuzumab for Breast Cancer, Gemtuzumab for AML, Alemtuzumab for CLL, and Cetuximab, Bevacizumab and Panitumumab for colorectal, non-small cell lung cancer and head and neck cancer. A few of these approved anti-cancer antibodies are conjugated antibodies, such as Ibritumomab and Tositumomab, which are radio-conjugates, and Gemtuzumab, which is an immunotoxin conjugated to the toxin ozagamicin.
Combination (Adjuvant) Therapy:
Modern cancer treatment protocols often combine more than one modality in order to both benefit from targeting of multiple aspects of the disease and reduction in dosage or duration of individual treatments, resulting in reduced frequency and severity of side effects. Combined chemotherapy and radiotherapy, or “cocktails” of chemotherapy drugs are commonly prescribed according to protocols assessing staging, treatment outcome and complications.
Trials of antibody and chemotherapy have indicated that some patients may benefit from combined therapy. Trials combining Bevacizumab (anti-epidermal growth factor) and oxaliplatin/capectabine or oxaliplatin/fluorouracil/leucovorin have indicated enhanced efficacy of treatment in some, but not all types and stages of cancer tested. Trastuzumab (anti-HER2/neu) and paclitaxel has been approved for use in breast cancer for many years, has been found effective in anthracycline non-responders, and is gaining popularity as first line breast cancer therapy. Clinical trials with colorectal anti-cancer antibodies such as 17-1A (anti-Ep CAM of small cell carcinoma) and Cetuximab (anti-VEGF) and chemotherapeutic agents such as oxaliplatin or irinotecan have demonstrated improved outcomes with some, but not all types and stages of cancer.
As CD24 expression has been implicated in many types of cancer, the combination of efficacious specific anti-CD24 antibodies and additional therapeutic modalities, either as separate physical entities or attached, is an important clinical goal for treatment and prevention of cancer, particularly colorectal and pancreatic cancer.